This invention relates generally to insulation methods and arrangements, and more particularly, to methods and arrangements for electrical and thermal stress management in an X-ray generator.
An X-ray generator (e.g., X-ray tube head) having a generator and an X-ray tube within a housing provides a compact source for X-ray generation in diagnostic medical imaging, industrial inspection systems, security scanners, etc. For high power X-ray generation, the X-ray generator may be operated at very high voltage, for example, more than 70 kV and at temperatures exceeding 200 degrees Celsius (C.) at the anode of the X-ray tube in an X-ray generator. Such operation may cause high stress zones having thermal and electrical stresses at the insulating material around the anode.
Known X-ray generators use insulating oil as a medium to provide insulation and also acts as a coolant to dissipate heat around the anode. However, the insulating oil may experience electro-hydrodynamic (EHD) forces resulting in strong electro-convection due to very high electrical stress, for example, around an anode. This may provide heat dissipation, but increases the likelihood of insulation breakdown. Moreover, oil insulation generally posses high sensitivity to particulate contamination and moisture that also may cause insulation breakdown. Furthermore, at the zone around the anode, X-ray photons may ionize the oil, thereby resulting in breakdown of oil at lower voltage levels.
Solid insulation also is known and provided as an insulating material to have high insulating strength. However, solid insulation typically has poor thermal properties compared to oil insulation.
Composite insulation configurations using solid insulation as a barrier in oil are often used to improve insulation strength. Although the composite insulation configuration improves insulation, it may not provide adequate heat dissipation.
Further, in X-ray applications, the geometry of the X-ray tube, particularly around the anode, which is at positive high voltage, and the surrounding casing at ground potential, often results in non-uniform electrical as well as thermal stress distribution. Non-uniform stress distribution results in a small volume of the medium experiencing very high stress and the rest of the volume experiencing much lower stresses. The electrical and thermal stresses are typically highest around the anode of an X-ray tube and reduces with increasing radial distance from the anode. Therefore, the material or oil around the anode is subjected to very high thermal and electrical stresses.
It is also known to provide a large clearance for insulation and cooling in an attempt to reduce high electrical and thermal stresses. However, this results in a much less compact system for high power applications.
Thus, these known insulation methods have limitations in use of insulation materials to efficiently manage electrical and thermal stresses around the anode of an X-ray tube and also fail to provide compact arrangement with a high degree of reliability for X-ray generators in continuous high power applications.